1. Field of the Invention
This invention relates to a light emitting apparatus and, particularly, to a flip-chip type light emitting apparatus that allows light radiated in the direction of an electrode-forming surface of LED element to be effectively used.
2. Description of the Related Art
Light emitting apparatuses are conventionally known that have an LED (light emitting diode) element being flip-chip mounted (herein called flip-chip type) and that use mainly light radiated in the direction of a transparent substrate, such as a sapphire, of the LED element.
Further, in order to enhance the light radiation efficiency, a flip-chip type light emitting apparatus (prior art 1) is known that is composed of: a support for mounting an LED element thereon; a conductive wiring layer formed on the support; and a light reflection layer of Al etc. formed on the wiring layer, so that light radiated in the direction of an electrode-forming surface of the LED element can be reflected by the light reflection layer.
On the other hand, Japanese patent application laid-open No. 9-298310 (prior art 2) discloses a flip-chip type light emitting apparatus that is composed of: a support for mounting an LED element thereon; a first electrode mounted on positive and negative electrodes of the LED element; and a second electrode formed on the surface of the support, wherein the second electrode is multilayered with a first layer formed on the support side, an intermediate layer and a second layer formed on the LED element side (FIG. 1 of prior art 2). The first layer is of a metal with good contacting property with the surface of the support, and the second layer is of a metal with good adhesion property with the first electrode. The intermediate layer serves to prevent the intermetallization between the first layer and the second layer.
However, in prior art 1, since the reflection layer is formed on the wiring layer, there may be generated an intermetallic compound between the reflection layer and the wiring layer. Due to the intermetallic compound, in etching process for making a wiring pattern (electrode pattern on the support), the etching rate will be reduced and thereby a residue will be generated between the wiring patterns. Such a residue causes deterioration in reliability such as short-circuiting. Further, due to the intermetallic compound, since a contact resistance between the reflection layer and a bump material to bond the LED element to the reflection layer increases, the emission efficiency of LED element will be reduced.
Although prior art 2 discloses the multilayered wiring layer structure to prevent the intermetallization, it is not directed to the use of a light reflection layer to enhance the light radiation efficiency.